Electric resistance heating element

ABSTRACT

A resistance heating assembly in which the heating element is a thin strip of apertured, foil-like material formed with a series of corrugations which establish a wavy or serpentine pattern. The heating element is supported by tubular insulators carried by a wire framework and located at the points of direction reversal of the serpentine pattern. The insulators are supported on wire members each having one end secured to the wire framework and a free end extending into a tubular insulator. The tubular insulators are secured against axial movement on the wire members but are rotatable relative thereto, whereby localized expansion and contraction of the strip is distributed over the entire length of the strip.

United States Patent 1191 Clement 1 Dec. 3, 1974 1 ELECTRIC RESISTANCEHEATING 3,651,304 3/1972 Fedor 219/375 x ELEMENT I 3,697,923 10/1972 Grift'cs 1 338/280 [75] Inventor: Jack M. Clement, Tecumseh, Mich. Primary Examiner A Bartis I 7 Assignee; Gould Inc. Chicago, 111 Attorney, Agent, or Firm-Edward E. Sachs 1 PP 328,856 A resistance heating assembly in which the heating element is a thin strip of apertured, foil-like material 52 us. c1 219/375, 219/381 219/532 fOhhed with a Series 0f corrugations which establish a Wavy or Serpentine pattern. The heating element is [51] Int CL Hosb 3/02 F2411 *3/04 H 3/00 supported by tubular insulators carried by a wire [58] Field of Search 219/374476 framework and located Points of direction versal Of the serpentine pattern. The insulators are 57 58 supported on wire members each having one end seh 3 cured to the wire framework and a free end extending I into a tubular insulator The tubular'insulators are secured against axial movement on the wire members [56] References cued T but are rotatable relative thereto, whereby localized UNITED STATES PATEN S expansion and contraction of the strip isdistributed 562,527 6/1896 Hadaway 61 al. 338/286 X ver the entire length of the Strip 870,611 11/1907 Beekley 1 338/280 946,544 1/1910 Harris 338/280 8 Clams, 5 Drawmg Figures 1,967,757 7/1934 Losec 219/375 X nee hhh be an PATENTELUEB' sum sum 10F 2- PAIENIELBEC 31w 3,852,568

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. l ELECTRIC RESISTANCE HEATING ELEMENT BACKGROUND OF THE INVENTION AND PRIOR ART tween two supporting members, or by using a coiled wire arrangement which is supported at intermediate locations by means of ceramic bearing mounts which surround the wire. I

The conventional coiled wire construction, however, has a low surface area and a high mass. The high mass leads to a relatively high raw material cost, while the low surface area leads to inefficient heating and cooling. As a consequence of the high raw material cost, a constant effort is made to minimize the amount of material used by deliberately operating the element at as high a temperature as possible, usually well into the red heat range. The operation of the element at the high temperature level has at least two detrimental consequences-the areas of low air flow (inside the ceramic bushings) become overheated and are prone to failure; and the efficiency of convective air heating is decreased as a significant amountof the energy is spent in radiant heating of the solids surrounding the element. The low surface area-tp-mass ratio also causes a slow heat-up and cooling rate.

Prior art self-supporting expanded metal stripswhich are secured between two supporting members are subject to excessive sagging at operating temperatures.

To overcome these disadvantages found in the prior art, a heating element has been proposed which is composed of corrugations establishing a wavy or serpentine pattern which provides at least the same electrical characteristics as prior art devices, but with a considerable saving in raw material. Such a device is set forth in U.S.'Pat. No; 3,651,304. According to that patent, a foil-like corrugated heating element is supported internally by a supporting rod having an electrically nonconductive surface which extends through the corrugations to constructurally support the strip at very short intervals. Since the strip is skewered by the support rod, it has a tendency to rotate about the rod and move axially relative to the rod.

Although these tendencies are not detrimental when the element is properly installed, careless handling prior to or during installing may tend to rotationally or axially displace the strip relative to the support rod. Axial displacement may tend to collapse some of the corrugations to contact an adjacent corrugation, thereby shorting out a portion of the circuit. Any rotational movement of the element relative to the support rod may cause the element to contact the surrounding housing structure.

A further disadvantage of a skewered strip assembly may be encountered when the strip is assembled on the skewer. Care must be taken to ensure that the projecting corrugations of the strip extend substantially uniformly from the skewer,- thus necessitating skewer penetration at substantially uniform intervals along the length of the strip. If one or more corrugations project beyond other corrugations, those projecting corrugations may touch the sidewalls of the structure in which the assembly is mounted.

SUMMARY OF THE INVENTION The present invention overcomes many of the disadvantages in the prior art by providing a resistance heating assembly comprising in combination a support framework, a plurality of insulators supported on said framework and located at the points of direction reversal of a serpentine path. Means coacting between the framework and each insulator are provided for supporting insulators in axially fixed relation. A thin strip of apertured, foil-like material is retained and supported by the insulators at intervals along the length of the strip, and is formed as a grid along the serpentine path. Electric terminal means communicating with each extremity of the strip are also provided.

According to one aspect of the present invention, the insulators are tubular and preferably rotatably supported by axially extending members which in turn are secured-to the support framework. Numerous advantages result from'rotatably mounting the tubular insulators. One resulting advantage is in the assembly of the device wherein the strip is threaded around the insulators in a serpentine path. The strip may easily be pulled through the device where there is rolling contact be- .tween the strip and the insulators. Another advantage obtains during operation of the resistance heating assembly, and particularly during those periods wherein the temperature of the strip is increased or decreased. Localized temperature increases may tend to expand and contract the strip in localized areas. If adjacent strip reaches are expanded, and if the ends of those reaches are substantially immobilized by frictional contact with the insulators, the expanded reaches may contact each other and short out the system. This is particularly true if the reaches are initially closely spaced. By rotatably mounting the insulators, localized expansion and contraction of the strip are distributed over the entire strip length.

Since insulators are provided at the points of direction reversal of the serpentine path of thestrip and the location of the insulators is fixed, there is no possibility of a corrugation extending beyond the predetermined space intended for the assembly.

These devices are also readily fabricated in modular design so that a plurality of resistance heating assembly units may be nested together to accommodate a given space heating requirement.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of a resistance heating assembly in accordance with one aspect of the invention.

FIG. 2 is a side elevation of the heating assembly shown in FIG. I, with portions of the heating element broken away for clarity.

FIG. 3 is a plan view of a heating assembly according to a further aspect of the present invention.

FIG. 4 is a partial end view of the heating assembly shown in FIG. 3, with portions broken away for clarity. and also illustrating indotted lines the assocation of a modular unit to yield a larger capacity structure.

FIG. 5 is a fragmentary cross-sectional view on an enlarged scale of one means of mounting the insulators orrto'the framework and as it would appear in'the plane indicatedby the 1ine5 inFIG. 3. "DETAILED DESCRIPTION OF THE INVENTION Referring now more particularlyto'the drawings, there is'shown in FIGS. I and 2 a foil-like strip l0'of commercially available material which'has electric resistancecharacteristics. This materialis more fully described in US Pat. No. 3,651,304, the disclosure of which is incorporated herein by reference. The strip is formed with a series of continuous and generally parallel extending corrugations 12 which establish in their totality a wavy or serpentine pattern.

According to the embodiment set forth in FIGS. 1

and 2 of the drawings, the strip, 10 isretained and supported by a, plurality of insulators l4. Insulators l4 are supported on a framework 16 which is conveniently formed of. wire members such as longitudinal side rails l8and 20, crosshead 22, end bar 24, and mounting plate 25. The insulators 14 are preferablyceramic insulators,and preferably include collars or flanges, such as flanges 26 and 28,'adjacent each extremity of theinsulator 14. The, flanges 26 and 28 are spaced apart a distance sufficient to accommodate readily the foil-like strip 10. The insulators l4 are-secured to the frame 16 in theembodiment shown in FIGS. 1 and 2 by means of U-shaped wire me'rnbers30. The U-shaped members embodiment wherein the serpentine path'is folded back upon itself to provide a relatively long, continuous heating element 10, the ends of which-are'disposed adjacent to each other atone end of the framework 16. In order to retain the tubular insulators l4'onto the upstanding legs 32 of the U-shapedsupports 30, the extremities of the legs 32 are conveniently bent at right angles to the legs 32 to form an abutment 36 of suffi cient length to prevent removal of the tubular insulating body 14.

As shown in FIGS. land 2, the U-shaped members 30 are disposed in parallel planes a relatively small distance apart and canted obliquely with respect to the longitudinal rails 18 and 20. The spacing between the U-shaped members 30 is desirably uniform, and may vary in accordance with the requirements of a particular installation. Thus, the distance between. the U- shaped members as disposed upon the rails 18 and 20, for example, may be varied in accordance with the structural requirements of the unit in which the resistance heating assembly will be disposed and in accordance with requirements for heat input to a moving gas stream. Where a large amount of surface area of resistance element is required, a folded structure such as isshown in FIGS. 1 and 2 may be employed. As will hereinafter appear, modular units of devices such as shown in FIGS. 1 and 2 may be nested together to increase the amount of heating element exposed to the moving gas I stream;

' In the embodiment shown in FIGS.*1and,2,the free ends-of the strip' 10 are suitably physically and electrically connected to terminals 40-and 42. Terminals 40 and 42 are suitably. mounted on acommon plastic insulating mount 44, which is in turn suitably secured to the mounting plate 25-. I Referring now to FIGS. .3, 4, and 5, there; is here 'shown another embodimentv of thepresent invention which is also characterized .by tubular insulating members, rotatably mounted on a framework and locatedat the pointsiof direction reversal of 1a serpentine path. Again, the apertured foil-like electric resistance material is woven so as to be formed with a series of continuous and generally parallel extending corrugations which in their totality establish a wavy pattern. In the embodiment shown in FIGS. 3, 4, and 5, the electric terminals, instead of being at the same end of the framework, are at opposite ends of the framework.

Referring to FIGS. 3 and 5 inclusive in greater detail, there is provideda wire framework 500i generally rectangular configuration and formed from longitudinally extending rods 52 and 54, each being rightangularly bentatthe extremities toward each other for communication andse'curernent to end plates 56 and 58. Twosuch'rec tangular structures formed from wire rods 52 and' 54, and from wire rods 52a and 54a, are provided in parallel relation to each other to define with the common end plates 56 and'58 a box-like'structure. Spacers 60 and 62span' the spaces between rods 52 and 54, for example, as shown in FIG, 3, to add rigidity to the structure. Additional spacers 60a and .a spacer obscured by'th e spacer 62 in FIGS. 3 arid-4 are provided. Inlike manhenvertical spacers 64, 66, 6 8, and maintain the longitudinal 'rods', such as 52 and 54, in proper parallel and spaced relation from the corresponding wire rods 52a and 54a;

A terminal74 extends through the end plate 56 and is insulated therefrom by any suitable means, such as insulating sleeve 76, and provided with a suitable binding post 78 for attachment of anv electrical lead. The inner extremity 80 of the terminal is suitably soldered or otherwise fastened to oneiend of the thin'apertnred foil-like resistance material. s I p The insulators l4shown in FIGS. 3,14, and 5 areof essentially the same structureas shown in .FIGS. 1 and 2, and are desirably rotatably mounted on inwardly extending axial members 82 and 84, for. example, which are welded to the rods, e.g., rods 52 and 52a, as shown in FIG. 5. Instead of split axles 82-84, continuous axle members may be used extending between rods 52 and 52a and betweenthe rods 54'and 54a.

As shown in FIG. 3, the opposite extremity of the assembly is also provided with a terminal 86 having an in sulating sleeve 88 and a binding post 90 extending through the end plate 58, and the thin strip of aper- J tured foil-like electrical resistance material is suitably affixed as by means of welding to an extremity 92 of the terminal. I I v v I i FIG. 4 is a fragmentaryend view of the embodiment shown in FIG. 3, and alsoshows a number of modular units arranged in nested form, as above indicated. To

secure adjacent modular units together, for example. there may be provided a simple band. 72 encircling the spacer bars such as spacer 60 and the corresponding spacer baron the next adjacent module. Several such encircling bands 72 may be required, and these may be of any convenient structure for the purpose.

As in the case of the device shown in FIGS. 1 and 2, the spacing between the insulating members is optional and depends upon the structural limitations of the device in which the assembly will be installed, as well as the output requirements for the structure. Heating elements in accordance with the present invention are readily adapted for mounting in electric clothes dryers.

While there have been described what are at present considered to be the preferred embodiments and aspects of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention,

- and it is intended, therefore, in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is: v

1. A resistance heating assembly comprising:

a. a support framework;

b. a plurality of tubular insulators supported on said framework and located at the points of direction reversal of a serpentine path;

c. means coacting between the framework and each insulator for supporting said insulators in axially fixed relation;

wherein the framework includes elongated wire member means and the insulator support means include a plurality of wire members each having one portion secured to said elongated wire member means and having a free end extending into a tubular insulator;

d. a thin strip of apertured, foil-like electrical resistance material retained and supported by said insulators at intervals along the length of said strip, said strip being formed as a grid along a serpentine path; and

e. electric terminal means communicating with each extremity of said strip.

2. A resistance heating assembly in accordance with claim 1 wherein the tubular insulators are rotatably supported.

3. A resistance heating assembly in accordance with claim 1 wherein the insulators are ceramic.

4. A resistance heating assembly in accordance with claim 1 wherein the said plurality of wire members of the insulator support means comprises a plurality of U shaped wire members secured to said framework at uniformly spaced intervals.

5.'A resistance heating assembly in accordance with claim 1 wherein the said plurality of wire members of the insulator support means comprises a plurality of U- shaped wire members welded at their respective bases to said wire member and having their free arms lying in planes obliquely disposed relative to said wire member and extending into said tubular insulators.

6. A resistance heating assembly in accordance with claim 1 wherein the elongated wire member means comprises a pair of parallel rectangular frames and means for spacing said frames.

7. A resistance heating assembly in accordance with claim 6 wherein the insulators are rotatably supported on said plurality of wire' members.

8. A resistance element in accordance with claim 7 in which the plurality of wire members consists of pairs of axially aligned rod members each secured to a different one of said rectangular frames and extending toward one another. 

1. A resistance heating assembly comprising: a. a support framework; b. a plurality of tubular insulators supported on said framework and located at the points of direction reversal of a serpentine path; c. means coacting between the framework and each insulator for supporting said insulators in axially fixed relation; wherein the framework includes elongated wire member means and the insulator support means include a plurality of wire members each having one portion secured to said elongated wire member means and having a free end extending into a tubular insulator; d. a thin strip of apertured, foil-like electrical resistance material retained and supported by said insulators at intervals along the length of said strip, said strip being formed as a grid along a serpentine path; and e. electric terminal means communicating with each extremity of said strip.
 2. A resistance heating assembly in accordance with claim 1 wherein the tubular insulators are rotatably supported.
 3. A resistance heating assembly in accordance with claim 1 wherein the insulators are ceramic.
 4. A resistance heating assembly in accordance with claim 1 wherein the said plurality of wire members of the insulator support means comprises a plurality of U-shaped wire members secured to said framework at uniformly spaced intervals.
 5. A resistance heating assembly in accordance with claim 1 wherein the said plurality of wire members of the insulator support means comprises a plurality of U-shaped wire members welded at their respective bases to said wire member and having their free arms lying in planes obliquely disposed relative to said wire member and extending into said tubular insulators.
 6. A resistance heating assembly in accordance with claim 1 wherein the elongated wire member means comprises a pair of parallel rectangular frames and means for spacing said frames.
 7. A resistance heating assembly in accordance with claim 6 wherein the insulators are rotatably supported on said plurality of wire members.
 8. A resistance element in accordance with claim 7 in which the plurality of wire members consists of pairs of axially aligned rod members each secured to a different one of said rectangular frames and extending toward one another. 